A*B Arms MOD X: The True ‘Drop-In’ Chassis

By Todd Burgreen

We are in the golden age when it comes to after-market gear available to enhance firearms. American Built Arms Company’s (A*B Arms) MOD X rifle chassis is an excellent case in point. The A*B Arms MOD X is a true drop-in chassis for Remington 700 Short-Action RH rifles; other MOD X variants are sure to follow considering the reception received for the Remington 700 MOD X. The decision to commence MOD X production with the Remington 700 Short Action cannot be questioned considering the propensity and following the Remington 700 rightfully enjoys.

The Remington 700 was first introduced in 1962. By 2007 nearly 4 million had been sold with 70 different factory variants offered and a myriad of special editions. The Model 700 was based on the Remington Model 40X. The 40X was a competition bolt action design. This lineage surely contributed to the Remington 700’s reputation for inherent accuracy. While the emphasis for the Remington 700 was economical production compared to its predecessors, its performance was not compromised. The action of this rifle is machined from a single piece of bar stock. As a part of the Remington 700’s design, the rifle has the infamous three rings of steel, meaning that the cartridge head while chambered is fully supported by three separate components. Over the years Remington has made much of this in its marketing efforts. The first component in the three rings of steel is the bolt face, which completely encapsulates the cartridge head. The second is the action end of the barrel, which the bolt face tucks into. This feature is especially important as it ensures that the bolt and the barrel are aligned correctly. The third ring of steel is the action itself, which the barrel threads into. All put together this makes for a very solid design, one that has withstood the test of time for 50 plus years.

As with all weapon systems time has caused a re-evaluation and search for performance enhancements with the Remington 700. While starting off as a sporting/hunting weapon, the Remington 700 soon found itself as the basis of U.S. sniping rifles beginning in the Vietnam War. The classic stock profile held sway for many years. This has given way of late to chassis systems that enable easy adaptation to high capacity detachable magazines, night vision and other mission-specific appendages. This is the focus of this article.

American Built Arms Company was founded in 2010. Jason Combs is the President and Founder of American Built Arms Company. He is a veteran with service in the U.S. Army 82nd Airborne Division. A*B Arms is committed to creating U.S.-made products for its customers. A*B Arms started out making parts and accessories for the AR-15 rifle. The company branched out to manufacture products for other firearms, such as the IWI TAVOR and AK. The parts quickly gained the attention of industry manufacturers for their quality and price point. A*B Arms made the decision to offer a rifle chassis after analyzing the existing market. After extensive prototyping and testing A*B Arms arrived at the MOD X.

It was decided to explore the MOD X via a colleague’s experience with one. A Remington 700 SPS with 16.5-inch barrel was purchased with the intent of installing it in a MOD X. A brief hiatus occurred when the rifle was returned to have the recoil lug centered properly in front of the action. The recoil lug being centered is a must to allow for proper install into the MOD X chassis. The problem was taken care of via a Remington service center.

Often users hear claims of “drop-in” only to find out that modifications and other types of machining work are necessary to get an after-market stock fitted properly. It was confirmed that all that was needed with the MOD X was a screwdriver with different bits or appropriate hex keys for use on various screws and fasteners. An adjustable torque wrench is also recommended, but not a necessity. The well done MOD X assembly manual lists specific torque wrench settings for the different fastener types for those inclined to follow directions. The MOD X chassis is intended for military, law enforcement and sportsmen. It offers a stock upgrade without having to resort to gunsmith custom fitting.

The MOD X delivers on providing a lightweight ergonomic modular stock that allows for users to easily configure as they see fit; i.e., bipod, tactical light, night vision, optics, etc. The MOD X weighs only 3 pounds, 10 ounces thanks to its aluminum construction. It is Mil Spec Type III hard-coat anodized. A 20MOA 1913 scope mounting rail is one integral feature appreciated by long-range shooters. Another enhancement is a 13.5-inch KeyMod forend that provides for a truly free-floated barrel that assists in maximizing inherent Rem 700 rifle accuracy. KeyMod slots are found on three sides of the forend with a standard 1913 rail on the top. Barrel diameters up to the same size of the action can be used with the MOD X chassis. A multi-point radial cut inlet is found in the MOD X for securing the action; not “V-block” bedding. This promotes a stress-free action enhancing accuracy.

The MOD X arrives with a fully adjustable Luth MBA buttstock. Other AR-type buttstocks can be fitted as well if desired. The same goes for the AR-style pistol grip. While outfitted with an A*B Arms SBR P-grip as standard equipment, any AR-type grip can be retrofitted. The A*B Arms pistol grip is made from high-heat-rated nylon with high strength fiber. The A*B Arms pistol grip offers a slim profile with unique ergonomics that need to be felt firsthand to be appreciated. All of these listed items make it clear that the MOD X is a true upgrade on many levels; however, one more remains to be detailed.

The MOD X is configured for the use of detachable MDT/AICS spec magazines—depending on caliber. There are multiple products on the market that seek to convert the Remington 700 rifles’ internal magazine into a detachable type. Frankly, most are problematic. The MOD X’s seamless integration of a detachable magazine makes it worthy of consideration in its own right even without all of the other enhancements. The MOD X’s mag well is designed to line up the detachable magazine’s lips with the Remington actions feed ramp. The MOD X chassis is configured to send rounds from the detachable magazine nearly directly into the chamber limiting the chance of feeding issues. It was crucial to eliminate any play forward or backward. Length tolerance within the MOD X magazine well is kept within +/-.0005. This is achievable via wire EDM machining techniques. This enables the action to be cycled rapidly without worrying about driving bullet tips into the feed ramp preventing chambering. Width tolerances were also considered with the MOD X chassis design. Too tight on the sides would cause problems with using both polymer and metal magazines. This is due to polymer magazines “swelling” when fully loaded, possibly binding it up. A*B Arms sought to split the difference enabling the use of multiple AICS spec magazines albeit polymer or metal.

Remington 700 Short-Action rifles are highly respected for their inherent accuracy. The MOD X allows this to be fully realized along with ability to configure as desired. Securely mounting an optic was made simple via the 20MOA rail above the receiver. Bipod attachment was possible via the KeyMod rail interface with placement options easily achieved along the bottom of the railed forend. The Luth MBA buttstock proved ideal for bench and prone shooting, riding support bags well while maintaining ability for offhand shooting; an important consideration for sportsmen or LE/military personnel in fluid operating conditions. The MOD X is lightweight compared to other chassis systems—key here. A*B Arms’ experience with the AR platform shines through with the MOD X by building in modularity via AR-compatible buttstocks and pistol grips. The use of a KeyMod forend is another example of this.

The Remington 700 SPS was first fired in the factory stock to establish a baseline of accuracy before installing in the MOD X. The author used 168-grain Federal Gold Medal Match, 168-grain Black Hills Ammunition Match, Winchester Match 168-grain and Hornady 168-grain Match. The pre-MOD X Remington 700 SPS produced 1 to 1 ¼-inch accuracy. Installation into the MOD X took place in Echo Valley Training Center’s training room. Thirty minutes later the MOD X was back on the firing line. Bolt manipulation was smooth and rapid when operated; operation with the detachable magazines was never an issue. The 10-round detachable magazine inserted and removed easily from the MOD X magazine well. The first group quickly showed potential with a three-round sub .5-inch cluster with Federal 168-grain Gold Medal Match. A*B Arms does not represent the MOD X necessarily as an accuracy enhancing method; though it often happens due to superior bedding and true barrel free float ability. Needless to say, shrinking groups by half was a pleasant surprise. While perhaps not typical, it showed potential of the MOD X chassis system.

The MOD X Modular Rifle System has been purchased by police departments, law enforcement snipers, long-range shooters, sportsmen and private security consultants who specialize in sniper operations. The feedback has been consistent praising the MOD X chassis light weight, ease in accessorizing as mission dictates, simple installation and quality construction. The fact that the MOD X is U.S.-made is appreciated as well. MOD X’s good looks with either the black or flat dark earth coloration are also mentioned. While Rem 700 Short-Action users are benefitting first, the MOD X chassis will definitely be offered in more variants to accommodate other rifle makes.


(A*B Arms)

This article first appeared in Small Arms Review V22N1 (January 2018)
and was posted online on November 17, 2017


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